1. Field of the Invention
The present invention relates to a nonaqueous electrolyte secondary battery. More particularly, the present invention relates to a manufacturing method of the battery.
2. Description of Related Art
A nonaqueous electrolyte secondary battery such as a lithium-ion secondary battery has been preferably used as a vehicle drive power supply for an electric vehicle, a hybrid vehicle, and the like, and a so-called portable power supply for a PC, a portable terminal, and the like, because the nonaqueous electrolyte secondary battery is lightweight and has a high energy density as compared with existing batteries.
In such a nonaqueous electrolyte secondary battery, improvement in a cycle characteristic (durability) is considered as a part of improvement in battery performance. As a related conventional technique, the abstract and the like of Japanese Patent Application Publication No. 2011-124086 (JP 2011-124086 A) describes that a cycle characteristic can be improved by using, as a positive-electrode active material, a lithium nickel cobalt manganese composite oxide including 500 ppm to 1000 ppm of sulfate radicals (sulfate ions) on surfaces of primary particles.
In the meantime, some nonaqueous electrolyte secondary batteries are required to have high battery characteristics (e.g., a cycle characteristic and input-output characteristics) under a wide temperature environment (e.g., −30° C. to 60° C.). Its typical example is a battery used as a vehicle-mounted high-output power supply. However, according to studies of inventors of the present invention, the battery as described in JP 2011-124086 A has such a problem that, in a case where a content of sulfate ions is high, for example, when an operating environment or a storage environment is maintained at high temperatures of 40° C. or more for a long term, a constituent element (typically, a transition metal element) is eluted from the positive-electrode active material, which may decrease battery characteristics.